A conventional derailleur gear system may be used on a bicycle for variating a running speed of the bike, which comprises a free wheel with more sprockets, a mechanism that alters the line of the chain and cause it to jump from one sprocket to another, and a tension pinion to take up or let out the slack in the chain for selecting various gear ratios for speed variation. However, such a conventional speed variation means has the following drawbacks:
1. Even so many sprockets are provided in the derailleur gear system, only two or three sprockets are used in a practical operation, thereby causing installation and maintenance inconvenience.
2. During the jumping of chain from one sprocket to another sprocket, the chain may be disengaged from the chain sprocket to influence a normal bike running.
3. A maximum speed or a minimum speed depends upon a diameter of the smallest sprocket or the largest sprocket. However, the diameter ratio of the largest sprocket to the smallest one is quite limited, thereby limiting a speed variating ratio of the bike.
4. The conventional derailleur gear system does not provide an automatic speed variation, thereby causing driving inconvenience.
Meanwhile, a conventional car of internal combustion engine has an automatic transmission which is operated by a hydraulic mechanism, being quite complex to thereby increase installation cost and maintenance problems.
The present inventor has found the drawbacks of a conventional speed variating means and invented the present automatic speed-variating means.